\[(10x - 5)^{2} - (8x - 3)^{2} + 4x =\]
\[= 36x^{2} - 48x + 16 =\]
\[= (6x - 4)^{2}\]
\[При\ x = 3:\]
\[(6 \cdot 3 - 4)^{2} = 14^{2} = 196.\]